Avoid Old Eggs When Hard-Cooking
Conventional wisdom holds that when making hard-cooked eggs, you should choose older eggs rather than fresh ones. Is conventional wisdom right?
Conventional wisdom holds that when making hard-cooked eggs, you should choose older eggs (such as those that have been sitting around in your fridge for a few weeks) rather than fresh ones. Why? Because they are supposedly easier to peel. Happily, our new method for hard-cooked eggs (see related content) makes any egg, whether just laid or weeks old, easy to peel. On top of that, we’ve learned that you are actually better off using fresh eggs over older ones for three specific reasons.
FLAT END: Because the air sac inside an egg becomes larger as the egg ages (that's why older eggs float), it can make the broad end of an older egg awkwardly flat. Fresh eggs, with their smaller air sacs, are more likely to have a smooth ovoid shape when peeled, which looks more appealing in applications as deviled eggs.
OFF-CENTER YOLK: Fresher eggs are more likely (though not guaranteed) to have centered yolks, again leading to more attractive deviled eggs.
MORE LIKELY TO FORM A GREEN RING: A freshly laid egg has a slightly alkaline white. As the egg ages, the white becomes increasingly alkaline. The more alkaline the white, the more quickly sulfur in the white reacts with iron on the yolk's surface when the egg is heated, forming the ferrous sulfide that creates the green ring in cooked eggs. While this green ring can be a symptom of overcooking, we confirmed that it is more likely to happen with older eggs. Fresh eggs could be cooked for a full 15 minutes (2 minutes past our cooking time) without forming a green ring, but the yolks of month-old eggs started turning green even within our recommended cooking times.
THE TAKEAWAY? When hard-cooking eggs, ignore conventional wisdom and go with the freshest eggs you can find. If in doubt, try looking at the “best if used by” date.